1. Field of the Invention
The present invention relates generally to a printing apparatus. More specifically, the invention relates to a printing apparatus performing a temperature control by employing a fluid.
2. Description of the Related Art
In a printing apparatus, temperature control of a printing head is important for improving printing quality. For example, in a printing head of an ink-jet system, when a head temperature or an ink temperature therein is varied associating with progress of printing operation, an ink ejection amount is also varied depending upon the temperatures. As a result, it may happen that printing is performed with different densities during printing operation. On the other hand, in the case of a thermal transfer type printing head, an ink amount to be transferred is varied associated with temperature variation. Thus, similarly, printing with different densities is performed.
On the other hand, as another example of lowering of printing quality, when a printing head has a plurality of printing elements, it is possible to cause non-uniformity of printing density even by non-uniformity of temperature to be caused between the printing elements. For example, in the case of a printing head of the ink-jet type, an ink amount to be ejected through ink ejection opening forming the printing element is differentiated between respective of individual ejection openings due to non-uniformity of the ink temperature. As a result, it is possible to cause density fluctuation and so forth on printed image or so forth. The non-uniformity of temperature to be caused between a plurality of printing elements tends to be relatively significant in so-called elongated head.
FIG. 14 is an illustration showing one example of a temperature distribution caused in an elongated head.
The shown head 1100 is an ink-jet type ejecting ink by utilizing thermal energy, which causes the distribution of temperature to have higher temperature at the center portion along the aligning direction of ejection openings 1101. The reason is that the ejection openings located at the longitudinal ends may have higher heat radiation effect.
In order to restrict lowering of printing quality due to distribution of the head temperature, there have been known various conventional constructions for controlling head temperature.
For example, it has been known to provide a sub-heater in addition to heaters for generating thermal energy to be utilized for ink ejection in an ink-jet head and to control driving of the sub-heater to adjust the head temperature (see Japanese Patent Application Laid-open No. 211045/1986). However, such construction for head temperature control is employed in a printer employing a head having the relatively small number of ejection openings, in general.
Contrary to this, in an industrial printing apparatus, such as an ink-jet textile printing apparatus and so forth obtaining a printing cloth and so forth by ejecting ink onto a cloth, for example, it is typical to employ an elongated head as set forth above to perform continuous operation for a long period, resulting in a large amount of heat generation in the head. Therefore, it is not possible to perform satisfactory temperature control by the construction for head temperature control to be employed in the typical printer. Accordingly, when the elongated head is to be employed, it has been required to perform temperature control by circulating a fluid, such as water or so forth through a part of the head to restrict elevation of the head temperature.